1. Field of the Invention
The present invention relates to a projection display apparatus including a scrambler for making a distribution of light intensity uniform.
2. Description of the Related Art
FIG. 1 shows a conventional projection display. The projection display includes an elliptical lamp 11 for converging light an a scrambler 13 for making a distribution of the amount of light emitted from the elliptical lamp 11 uniform. A relay lens 15 illuminates the light toward a liquid crystal display (LCD) panel 19. A collimator lens 17 which is positioned between the relay lens 15 and the LCD panel 19, collimates the light incident from the relay lens 15 in parallel form. The collimated light contains a video signal displayed by means of the LCD panel 19. In FIG. 1, character "A" denotes a focal length of the lamp 11, character "B" denotes the length of the scrambler 13 and character "C" denotes a focal length of the relay lens 15.
The conventional projection display shown in FIG. 1 uses only the scrambler 13 in order to make uniform the distribution of intensity of the light emitted from the elliptical lamp 11. However, when the light entering the scrambler 13 has a large angle of incidence .theta..sub.0 with respect to the scrambler 13, the light emerging from the scrambler 13 has a large angle of emergence .theta..sub.2 with respect to the scrambler 13. Consequently, the light emerging from the scrambler 13 has a large angle of divergence.
As a consequence of the large angle of divergence, the size of optical elements, such as a dichroic mirror and a relay lens, used for illuminating the light diverging from the scrambler 13 at a large angle towards a display panel, such as LCD panel 19, without loss of light is increased. As a result optical design becomes difficult. Also, as the angle of emergence .theta..sub.2 of the light emerging from the scrambler 13 is enlarged, the angle of incidence of the light incident to the surface of the LCD panel 19 is also enlarged, even through the light passes through the collimator lens 17. As a result, the angle of divergence of the light having passed through each pixel on the surface of the LCD panel 19 is enlarged, which lowers the contrast of a picture on the LCD panel 19.
To solve the above defect of the conventional art, the angle of incidence .theta..sub.0 of the light emitted from the lamp 11, with respect to the incident surface of the scrambler 13, should be reduced. This would thereby reduce the angle of emergence .theta..sub.2 of the light emerging from the scrambler 13 .